Further
Gliding and Wind Tunnel Experiments - 1901

The
Wright brothers were so enthused about returning to their flying in the
summer of 1901, that they hired Charlie Taylor, a talented machinist,
to take care of the repairs and sales in their bicycle shop in Dayton.
Their sister Katharine was lined up to manage the company, allowing Wilbur
and Orville to return to North Carolina in early Julythe middle of the
cycling season.

Kiting the 1901 glider.

A
bottom view of the 1901 glider.

They
took the makings of a new 22-foot (6.7-meter) wingspan machine with them.
This time the brothers set up their camp near Kill Devil Hills, four miles
south of Kitty Hawk and also sunk a well. It took them several weeks to
build the new glider and
hangar in which to store it.To provide more lift, its wing surface was almost twice the area of their 1900 glider. The glider's total surface area was 315 square feet (28 square meters), including the elevator, and was the largest glider ever flown.
It also incorporated a foot actuated wing-warping control system that the pilot used to turn the aircraft. The brothers also made sure the wing camber
matched Otto Lilienthal's
calculations.

Two
flying enthusiastsEdward Huffaker and George Sprattjoined the
brothers. Octave Chanute,
the Wrights-friend, thought the two could benefit from the experience
by helping Orville and Wilbur. With these guests arrived a huge swarm
of aggressive mosquitoes-making all their lives there miserable. When
Chanute arrived at the camp a few weeks later, he brought extremely fine-meshed
mosquito netting with him .

Huffaker,
Chanute, W. Wright, and Spratt

The
1901 glider in flight.

The
1901 glider

Wilbur
and Orville began another season of flying, but the new glider did not perform nearly
as well as the first. The glider would nose-dive into the ground, and,
once, only the front-located elevator saved Wilbur's skin. The brothers
realized how Lilienthal had been killed when his glider crashed on his
final flight. They began questioning the validity of Lilienthal's aerodynamic
calculations they were using and suspected Lilienthal's data for camber
contributed to the problem. They reverted to the wing camber of the previous
year, which resulted in more successful glides, but that still did not
solve the problems they were experiencing with the craft's lift to drag
ratio.

A
close-up of Wilbur.

Although
the brothers succeeded in making one flight of 389 feet (120 meters), outdistancing
Chanute's gliders of 1896, they decided to return to Dayton and perform
their own calculations for airfoil
lift and drag. They left North Carolina feeling pessimistic about their
efforts. At the time, Wilbur made the prediction that men would sometime
fly, but it would not be within our lifetime. Orville's recollection
of Wilbur's comment was, "Not within a thousand years would man ever
fly."

Back
in Dayton, they felt almost ready to abandon aeronautics. They were saved
by an invitation that Chanute sent at the end of August 1901, inviting
them to speak at the distinguished Western Society of Engineers meeting.
Although Wilbur had to be persuaded to accept the invitation by his sister,
he found that preparing for the speech forced him to examine everything
that had occurred up to that time. Wilbur's speech, titled 'Some
Aeronautical Experiments,' was made to an appreciative crowd of society
members and their wives, and showed slides of his machines in the air.
He also suggested that Lilienthal's lift and drag tables were wrong.
Once Wilbur had publicly stated they felt that Lilienthal’s data
was wrong, they had to find a way to determine the correct data. They
devised an unconventional testing machine that called upon their bicycle-making
talents.

Wrights'
unconventional testing machine.

Peter
Jakob says it best: "They mounted two small surfaces vertically on
a bicycle wheel laid on its side. The wheel was free to turn in response
to the wind striking the surfaces. One surface was a flat plate mounted
perpendicular to the flow. The other was a model wing patterned after
the curve used by Lilienthal.
According to Lilienthal's table, the model wing set at a five-degree angle of
attack would generate enough lift to balance the flat plate exactly."
Exposing the device to the natural wind did not yield good results, "so
the Wrights mounted the horizontal wheel to the front of a bicycle to
create a steady flow." [1] In a steady
wind, which was produced by riding the bicycle up and down the streets
of Dayton as fast as possible, the lift generated by air rushing over
the surface of the curved airfoil would be balanced against the drag on
the flat airfoil. If the lift on the curved airfoil and the drag on the
straight airfoil were equal, the wheel would not revolve. If the lift
were greater than the drag, the wheel would revolve in one direction;
if the drag were greater than the lift, it would revolve in the other
direction.

They
set the curved airfoil at the angle stated in Lilienthal's tables. The
wheel revolvedproving the lift and drag were not equal and the drag
exceeded the lift that was generated. An error existed either somewhere
in Lilienthal's work or the multiplier he had used in his equation to
describe lift, called Smeaton's coefficient,
was incorrect. This number, with a value of 0.005, had been developed
by the 18th-century English engineer John Smeaton to design windmills
and had been accepted as true for almost 150 years.

The
wind tunnel.

The wind tunnel.

The
wind tunnel.

Although
their device indicated that something was amiss, it was too crude for accurate
measurements, so the brothers designed and constructed a wind tunnel
to double-check the results of the bicycle-wheel experiment. This wind
tunnel consisted of a square tube for aiming the air, a fan that drove the air, and a balance mounted in the airstream. The preliminary results
from this tunnel were so promising, the brothers built a second, larger
apparatus with a square test section 16 inches (103 centimeter) on a side. This tunnel
produced the critical data they needed for their 1902 glider and the powered
aircraft that would follow.

During
late October and early November, Orville and Wilbur conducted tests on
some 200 different wing shapes in the tunnel. These tests served
primarily to validate and perfect the operation of the tunnel. By November
22, they were ready to carry out their formal tests that would prove to
be so important.

Wind
tunnel test results were recorded on scraps of wallpaper.

The
brothers also devised a lift balance.

Wind tunnel results compiled
in otebooks.

They
used 38 different model airfoils for these tests. These
airfoils had an assortment of cambers, thickness, and shapes, including
squares, rectangles, ellipses, uneven tips, and half circles, which they
tested in different combinations. They tested single-wing and multiple-wing
configurations. It was tedious and exacting work, requiring each wing shape be tested at 45
different angles. But by mid-December 1901, they had discovered, much
to their surprise, that Lilienthal's tables were largely correct. It was
Smeaton's coefficient that was wrong. The brothers also found the camber,
or curvature, of Lilienthal's wings was inefficient. To remedy this, they
designed wings with more of a parabolic curve that placed the high point
of the wing about one-fourth of the way back down the chord from the leading
edge rather than at its center, as Lilienthal had.

There
was one other area where they had erroneously relied on Lilienthal's tables.
They did not correct for the differences in the aspect ratio between Lilienthal's
wing and the wings of their gliders. In other words, the proportion between
the wingspan and the wing's chord length
was different. This also affected the amount of lift generated.

Wilbur
and Orville spent the rest of 1901 using their wind tunnel to answer some
remaining questions regarding the shape and location of the wings. Through
their methodical approach, they had achieved what no one had done before
and answered questions that had remained unanswered for years. The brothers
were sure they were right. Now they were ready to return to Kill Devil
Hills and fly.

Educational
Organization

Standard
Designation (where applicable)

Content of
Standard

National
Council for Geographic Education

Standard
1

How to use
maps and other geographic representations to acquire and process information.

International
Technology Education Association

Standard
10

Students
will develop an understanding of troubleshooting and experimentation in
problem solving.